Project Summary/Abstract This project ties together and explores three noteworthy trends that have taken place in the U.S. over the past two decades: (1) The gestational age distribution of full-term births (almost 90% of births in the U.S.) has been changing: Those at 40 and 41 weeks decreased by 11% and 38% respectively, while those at 37, 38, and 39 weeks increased by 31%, 27%, and 41% respectively. (2) Rates of caesarian section (C-section) delivery rose 44% and inductions of labor increased by 150%; C-sections now account for over 1/3 of all births and almost 1/4 of births are induced. The rapid increases over the past decade in particular coincided with no improvements in fetal, infant, or maternal mortality and are substantially higher than what would be expected based on trends in risk factors, suggesting that in many cases these interventions (which can shorten gestation) are not medically necessary. There has been speculation that changes in the gestational age distribution have resulted from increases in ?elective? (non- medically necessary) C-sections and inductions, but this allegation has not to date been tested. (3) Cognitive and behavioral disorders such as ADHD, learning disabilities, and autism have increased substantially over recent decades, and recent research indicates that shorter gestation, even by one week within the ?full term? range, leads to increased risk for adverse neonatal morbidities that are associated with childhood cognitive and behavioral disorders. We will use unique linked vital statistics data from the states of NJ and CA to advance our understanding of how these 3 noteworthy trends are related by: (1) Documenting trends and patterns in gestational age (GA) and method of delivery in low risk term pregnancies and conducting analyses of spatial diffusion of ?elective interventions.? (2) Estimating effects of GA, method of delivery, and their interaction on autism and other developmental outcomes in low risk term pregnancies and assessing the contributions of changes in GA and delivery methods to trends in child disability. (3) Exploring salient neonatal outcomes as pathways. This project will provide important, timely, and policy-relevant information with high relevance for healthcare delivery and population health.